Admin registration process

[rednaks]

We need an admin registration process,
I'll draft something.

[rednaks]

[rednaks]

I think we should avoid the registration of the first admin from the web interface, and create the admin at the initialization.

[rednaks]

New registration process

[rednaks]

Note that the activation should be done by an other active admin, this is discussed in #93

[rednaks]

for anti-spam purpose, the registration form page should be only accessible after a persona login attempt.